|To determine the numeric aspect of an interval, count the lines and spaces. We don't even need to know the clef to do this. We do have to remember when counting intervals the first note is 1. When counting steps the first note is 0 (zero).
The interval of 1, that is notes with the same letter name, is called a unison. An interval of 2 is called a "second", 3 - "third", 4 - "fourth", 5 -"fifth", 6 - "sixth", 7 - "seventh" and 8 - "octave". Intervals of a ninth to a thirteenth are often named but intervals over two octaves (fifteenth) are referred to by the number of octaves plus the remainder (the piano keyboard has a range of seven-octaves and a minor-third).